This disclosure is related to compositions comprising magnesium borohydride, and methods for preparing such compositions.
Hydrogen is a “clean fuel” because it can be reacted with oxygen in hydrogen-consuming devices, such as a fuel cell or a combustion engine, to produce energy and water. Virtually no other reaction byproducts are produced in the exhaust. As a result, the use of hydrogen as a fuel effectively solves many environmental problems associated with the use of petroleum based fuels. Safe and efficient storage of hydrogen is, however, essential for many applications that can use the hydrogen fuel. In particular, minimizing volume and weight of the hydrogen storage systems are important factors in mobile applications.
Several methods of storing hydrogen are currently used, but these are either inadequate or impractical for widespread mobile consumer applications. For example, hydrogen can be stored in liquid form at very low temperatures. However, the energy consumed in liquefying hydrogen gas is about 30% of the energy available from the resulting hydrogen. In addition, a standard tank filled with liquid hydrogen will become empty in about a week through evaporation. Thus, dormancy is also a problem. These factors make liquid hydrogen impractical for most consumer applications.
An alternative is to store hydrogen under high pressure in cylinders. However, a 100 pound steel cylinder can only store about one pound of hydrogen at about 2200 psi, which translates into 1% by weight of hydrogen storage. More expensive composite cylinders can store hydrogen at higher pressures of about 4,500 psi, using special compressors to achieve a more favorable storage ratio of about 4% by weight. Although even higher pressures are possible, safety factors and the high amount of energy consumed in achieving such high pressures have compelled a search for alternative hydrogen storage technologies that are both safe and efficient. In view of the above, there is a need for safer, more effective methods of storing and recovering hydrogen.
Magnesium borohydride, Mg(BH4)2, is a promising material for hydrogen storage and recovery. It comprises up to about 14.8 weight percent (wt %) of hydrogen that can be liberated upon heating. The use of magnesium borohydride is limited by the absence of convenient methods for its manufacture. It is therefore desirable to have a convenient method for manufacturing magnesium borohydride.